Catalytic conversion of hydrocarbons



Aug- 19, 1941- A. BELcHETz 2,253,486

CATALYTIC CONVERSION 0F HYDROARBONS Filed May 20, 1939 2 Sheets-Sheet l Aug 19, 1941- A. BELcHETz 2,253,486

CTALYTIC CONVERSION 0F HYDROCARBONS Filed May 20, 1939 2 Sheets-Sheet 2 REGENERH To@ /05-50 cnr/7L Ys T ATTORNEY Patented Aug. 19, 1941 oA'rALYTrc coNvEasroN oF cannons mao- Arnold Belchetz, Kew Gardens, N. Y.

Application May 20, 1939, Serial No. 274,670

8 Claims.

The present invention relates to the catalytic conversion of hydrocarbons into lighter hydrocarbons of lower-boiling point or hydrocarbons otherwise altered in structure. More particularly, my invention relates to the catalytic conversion or cracking of high-boiling petroleum oils to low-boiling products, and the catalytic reforming of petroleum oil fractions such as naphtha and gasoline.

The catalytic conversion of hydrocarbons involves, in general, two stages, a conversion stage wherein the hydrocarbons undergoing treatment are contacted with the catalyst under conditions adapted to effect the desired conversion, and a regeneration stage wherein the carbonaceous deposit formed on the catalyst during the conversion stage is eliminated. In its preferred aspect, my invention contemplates particularly an improved process involving a conversion stage wherein the hydrocarbons undergoing treatment are passed through the conversion zone in the form of vapor having the catalyst in finely divided condition suspended therein; and a regeneration step wherein used catalyst, after separation from the gaseous conversion products, is suspended in oxygen-containing gas and carried thereby through the regeneration zone to regenerate it by burning off deposited carbonaceous material.

This method of catalytically converting hydrocarbons has certain advantages arising particularly out ofthe relative intimacy of contact which it affords between the suspended catalyst and the carrier gas both in the conversion and regeneration operations. various disadvantages the elimination of which is one of the primary objects of my invention. One of these disadvantages obviated by my'invention, resides in the difficulty of satisfactorily controlling the regeneration reaction in such manner as to eliminate the carbonaceous deposit on the catalyst to the desired extent without overheating of the catalyst. A further object of my invention is the provision of a procedure for heating and vaporizingthe hydrocarbon preparatory to its passage to the conversion zone under such conditions `as to avoid undesired thermal decomposition effects and the accomplishment of this result by the direct utilization of the heat of regeneration.

Another object of the invention is the provision of a process whereby the removal of deposited carbonaceous material may be effectively controlled in the regeneration stage in such manner as to leave a predetermined quantity thereof It exhibits, however,

on the catalyst. Various other objects and advantages of my invention will be evident to those skilled in the art as the description thereof proceeds.

One of the features of my invention whereby the above objects are attained, resides in the charging of the catalyst and hydrocarbon feed to the conversion zone in proportions which are markedly different and advantageous compared with those indicated by conventional practice. In such practice, this ratio is determined primarily on the basis of the activity of the catalyst and the extent to which deactivation thereof occurs during the conversion stage, the objective being, in general, kto limit the quantity of catalyst employed to the smallest feasible amount consistent with the production of the desired extent of conversion, both because of the cost of the catalyst and processing costs incident to its circulation. Limiting factors with respect to the proportion of the catalyst thus employed relative to the hydrocarbon charged, are' the total carbonaceous material deposited during the conversion of a given amount of feed to the desired extent, and the quantity of carbonaceous deposit which the catalyst is capable of carrying before its activity drops to a point where its continued use is not feasible or desirable.

Within the limits determined by the foregoing,

conventional practice has been to maintain the quantity of catalyst introduced to an amount as low as possible. In accordance with my invention, in contradistinction to such practice, a relatively high proportion of the catalyst is preferably maintained relative to the hydrocarbon charged.

An additional'feature of the invention involves the mixture of the hydrocarbon feed with preheated catalyst, preferably `at a vtemperature sufficient to vaporize'the feed, the necessary preheating of the catalyst preferably being effected in the regeneration reaction. In one distinctive embodiment of my invention the heating and vaporization of the feed effected by the admixture of preheated catalyst therewith may be supplemented by the mixture of hot combustion gases derived from the regeneration operation with thefeed.

Another feature of my invention Ainvolves the controlled combustion of the used catalyst in such manner that a predetermined quantity of carbonaceous material is left thereon. y

The various featuresof my invention are interrelated in such manner that their conjoint use is desirable. However, various features thereof are susceptible of application independently of the others, as will be apparent to those skilled in the art.

The foregoing and various other features of Vthe invention will be apparent from the followmixing the feed stock with combustion gases from the regeneration zone.

Referring to the drawings, the feed to the system, for example, a reduced petroleum crude, enters from any convenient source indicated by the numeral I and is pumped by pump 2 to a heater or furnace 3 wherein it is preheated to a suitable temperature and then flash evaporated in evaporator 4. The volatile portion of the crude is taken overhead from evaporator 4 as a gas oil fraction through line 5 and a heavy residual fraction withdrawn from the process at the bottom through line 55. From line 5 the gas oil vapors pass through a heat exchanger 6, then through a condenser coil 'I into accumulator 8. Steam introduced through line 9, is condensed together with the gas oil and separated therefrom in accumulator 8 through line I0. The gas oil condensate is pumped by pump II through line I3 to heat exchanger 6 and into line I2. Part of the gas oil is returned as reflux to the evaporator through line I4.

The apparatus described above is merely illustrative of conventional apparatus for supplying the gas oil or other treated hydrocarbon at a suitable temperature for the following conversion operation.

The preheated fresh feed in transfer line I2 may be advantageously combined with a hot recycle oil introduced through line I4, the combined streams passing to the conversion stage through lineV I5. The oil passes through line l5 into pipe I6 constituting an extension of the conversion reactor I1. Hot preheated catalyst is supplied from in collecting or surge drum I8 by helical feeder I9 and mixed with the oil in pipe I6. The upper surface of the body of catalyst in drum I8 is indicated by dotted line 60. 'I'he quantity and temperature of the catalyst are sufficient to cause vaporization of the oil thereby forming a suspension of the catalyst in the vapors. Sufficient steam or other suitable gas to initially disperse the catalyst as discharged from feeder I9 is preferably introduced through line 20. Steam or other suitable gas may be supplied in greater quantities through line 20 when required to supplement the vapors resulting from the vaporization of the feed stock to produce the required volume of gas to carry the catalyst through the conversion reactor I1. The ratio by weight of the catalyst to fresh feed stock is maintained and regulated pursuant to my invention as set forth in detail hereinafter. The gaseous mixture of feed stock, catalyst and steam flows upwardly through reactor I1 during which flow conversion or cracking of the oil to the desired extent occurs.

separator such as a cyclone type of dust collector 25 wherein most of the remaining suspended catalyst is separated and then passed to tower 23 by gravity flow from the bottom of the separator through line 26.

Tower 23 serves to displace hydrocarbon vapors contained in the voids between the particles of catalyst and is suitably provided with baffles 21 to effectively expose the catalyst passing downwardly therethrough to the displacing action of a countercurrently flowing current of steam introduced at the base of the tower through line 28. Steam containing the oil vapors displaced from the catalyst is withdrawn from the top of the tower through line 29 and combined with the vapor stream from tank 2|. Used catalyst falls from the bottom of tower 23 into a surge drum 30. The gaseous suspension withdrawn from separator 25 containing the gaseous conversion products, steam and a small residual amount of used catalyst, is passed through line 3| to a suitable type of fractionator 32 wherein a low-boiling fraction such as gasoline and fixed gases may be separated from the high-boiling products such as light and heavy cycle gas oils. In fractionator 32 the conversion products may, for example, be fractionated into a low-boiling fraction including gasoline and fixed gases withdrawn as the overhead product from the fractionator through line 33, an intermediate product such as light gas oil withdrawn as a side cut through line 34, and a residual high-boiling fraction such as heavy recycle gas oil withdrawn through line 35, cooled in cooling coil 6I and pumped to storage through line 38.

In the bottom of fractionator 32 suitable means may be provided for separating residual catalyst present in the vapors introduced through line 3l. As shown, these means comprise a. line 31 through which a portion of the high-boiling fraction withdrawn through line 35 is returned to the fractionator over baflles 36 which deflect the vapors from line 3l into intimate contact with the returned fraction which consequently adsrbs or scrubs out residual catalyst present in the vapor. After passing over bales 36 the scrubbing liquid collects in the bottom of fractionator 32 from which it is withdrawn through line 39 and pumped by pump 40 into line I4 for utilization as a recycle oil, as previously described.

Used catalyst is fed from drum 30 (in which the upper surface of the catalyst mass is indicated by dotted line 62) by screw feeder 4I to pipe 42 and carried therein by a current of oxygen-containing gas such as air injected through line 43 to regeneration or combustion chamber 44 in which combustion of the carbonaceous deposit on the spent catalyst occurs during the passage of the catalyst therethrough. Steam may be introduced when desired through line 45. The proportion of oxygen-containing gas injected relative to the quantity of used catalyst is preferably maintained and regulated, hereinafter in detail.

Combustion gases bearing the regenerated catalyst pass from chamber M into a suitable recovery system for separating the catalyst. As shown, this system comprises a settling tank 46 wherein most of the catalyst is separated and ows downwardlytherefrom through conduit 41 to surge drum I8. The separated gases containing a small residual amount of catalyst fines leave separator 46 at 'the top through line I8 and pass to a cyclone type of dust collector 49, whereas described .in substantially complete separation of the catalyst is effected. The separated catalyst from collector 49 then flows downwardly through line 50 and is combined with the initially separated catalyst in drum I8 from which it is fed directly .to the conversion stage by feeder I 9, as previously described. Drum I8 and feeder I9 may be suitably provided with heat insulation material to obviate loss of heat by the regenerated catalyst in its passage therethrough.

Suitable apparatus for an alternative type of flow is indicated by Fig. 2. In this embodiment the total products of regeneration including both the hot catalyst and combustion gases are introduced directly to and mixed with the feed stock prior to its passage to the conversion zone. The

proportion of oxygen-containing gas to used catalyst introduced to the regenerator employed in the practice of this embodiment is preferably regulated in a specic manner as described hereinafter.

The elements of the system shown in Fig. 2 are similar to that of Fig. 1 with the exception of the regeneration chamber M', and are numbered with similar reference numerals. The regenerated catalyst and regeneration gas in place of being separated in a separator 46, are passed downwardly through the left arm of chamber 44' and are mixed with the oil introduced through I5.

The range of catalyst-to-oil-feed ratio employed in accordance with my invention and other preferred processing conditions, is illustrated by the following examples.

In one example, a petroleum gas oil having a gravity of 31.4 A. P. I. was used as the feed stock to be catalytically converted or cracked by the process to a low-boiling stock having a required amount of hydrocarbon within the gasoline boiling range. This particular gas oil was produced by the ash evaporation of a reduced crude and' constituted the volatile portion thereof amounting to about 90% of the crude charged to the evaporator. In the process of converting this particular oil t the desired extent, it was determined that coke or carbonaceous material appearing as a deposit on the catalyst would be produced to the extent of v3.5% by weight of the charged gas oil. A temperature of 865 F. was chosen as representing a suitable mean temperature for the reaction which, since the conversion reaction is endothermic, corresponded to an inlet temperature to the reactor of about 880 F., and an outlet temperature of 850 F. The deactivation temperature of the particular catalyst employed was ascertained to be approximately 1000 F., this temperature'being the maximum temperature to which the-catalyst could be subjected under the regeneration conditions without substantial destruction of its catalytic activity.

Pursuant to my invention, in xing the ratio by weight; of the catalyst charged to the fresh gas oil charged, for this particular oil and extent of conversion required, this ratio was determined in a manner adapted to assure the presence ofthe catalyst in suiilcient amount to absorb a definite minimum amount of the heat of regeneration, this ratio R being determinable by the application of a generalized formula derived by the application of the principles of my invention, asfollows:

R sm-T2) K In this formula, R, represents the catalyst-to-oil weight ratio; the symbol C, the fraction oi.' the gas oil or other hydrocarbon charged, converted to coke or carbonaceous material and deposited on the catalyst during the conversion; H, the heat of combustion of the coke or carbonaceous material expressed in B. t. u.s per 1b.; S, the specific heat of the catalyst; T1, the deactivation temperature in degrees Fahrenheit of the catalyst; T2, the temperature in degrees Fahrenheit of the catalyst on entering the regeneration zone; and K, a fractional coefficient having a lower limit determined by the extent to which expedients other than the heat absorption capacity of the catalyst may be employed to dissipate the heat of regeneration. Considering the conditions obtaining in the regeneration zone in the practice of my invention, it is evident that the ratio (r) between the catalyst charged to the regeneration zone and the oil charged to the conversion zone is equal to R and is definable likewise by the above formula.

In this particular example, the regeneration was effected in accordance with the preferred embodiment of my invention wherein sufiicient air was supplied to the regeneration zone to supply only the theoretical quantity of oxygen required to burn off the carbonaceous material to the required extent and without the provision of any means to absorb the heat developed during the regeneration other than the heat absorptive capacity of the catalyst and combustion gases. For these conditions, it was determined that K should have a value of approximately .83. The value of C, H, S, and T1, for this particular example, were xed by the specic characteristics of the' conversion and substances concerned, and were respectively, 0.035; 16,400; 0.22; and 1000. Since the used catalyst may be advantageously transferred directly from the conversion zone to the regeneration zone without substantial intermediate cooling in accordance with my invention, which procedure was followed in this instance, the value of T2 corresponded approximately to the outlet temperature of the conversion zone, namely, 850. Accordingly, substituting these values for the corresponding symbols in the above formula it is evident that the maintained catalyst-to-oil weight ratio, R, is equivalent to the ratio,

By the maintenance of the catalyst-to-oil ratio at the relatively high value of 14.5, as determined above, the absorption of the heat of regeneration at a temperature below the deactivation temperature of the catalyst, was'readily and effectively accomplished solely through the medium of the heat absorption capacity of the catalyst and the combustion gases without the use of extraneous cooling means.

It is to be noted that the ratio as above determined, is not sharply critical and may be increased or decreased Without departing from the characteristic features of my invention, these variations in general corresponding to permissible variations in the numerical limits of the coefcient K. In the above specic example, for instance, the catalyst-to-oil ratio may be maintained at a larger figure than 14.5, thereby assuring the circulation of a quantity of catalyst not only sufcient but in excess of that needed for the desired minimum absorption of heat by the catalyst during the regeneration reaction. The amount of such surplus catalyst will normally be controlled by economic considerations dependent upon the cost of the surplus catalyst and the processing expense incident to its circulation. Since these factors will normally outweigh any advantage to be gained by the circulation of surplus catalyst, it is contemplated that the practice of my invention will usually and preferably be practiced with a catalyst-to-oil ratio wherein K has a value not very greatly in excess of that `employed in the above example.

The catalyst-to-oil ratio, as above determined, may also be decreased to some extent, such changes corresponding to the lower limiting value of the coeliicient K. For example, the use of a lower ratio and corresponding lower K value may be feasible through the use to a limited extent of cooling coils or similar extraneous catalyst that the value of K, will be greater than 0.2 and preferably greater than 0.5.

In the conversion of the gas oil used in the above example, the procedure followed was that previously described in connection with the appended drawings, the catalyst-to-oil ratio being maintained at a minimum of 14.5 to 1, as above determined, and air being introduced through line 43 in quantity suflicient to supply only the theoretically required amount of oxygen to burn ol or reduce the concentration of the carbonaceous deposit to the desired extent; also fthe hot regenerated catalyst was withdrawn from drum I8 and thereafter mixed with the feed stock without any substantial intervening cooling, and contained sufiicient heat to vaporize the feed stock introduced at a temperature of about 550 to 600 F. at the pressure maintained in the reactor of 25 lb. gauge. In this particular example the feed stock consisted of about 85% gas oil feed introduced through line l2 at a temperature of 550 and about 15% of the heavy recycle fraction introduced through line I4 at a temperature of 600 F.

Also, in this example, air was admitted to the regeneration zone in 'amount sufficient only to lreduce the concentration of carbonaceous deposit to 1.5% by weight of the catalyst, and consequently the catalyst was circulated at all times with a minimum amount of carbonaceous material thereon amounting to 1.5% by weight of the catalyst. In passing through the conversion zone the carbonaceous material concentration on the catalyst under the conditions of this particular example increased to 1.74% and accordingly in the regeneration stage the carbon concentration of the catalyst was reduced from 1.74% to 1.5%.

The maintenance of a definite minimum concentration of carbonaceous material on the catalyst as exempliiied by the above example, has important and distinctive advantages. It assists in the regeneration reaction since the rate of combustion is accelerated and more readily controlled by the presence of an amount of carbonaceous material in excess of that which is to be removed by combustion. The retention of residual carbonaceous material also makes it possible to discharge the regeneration combustion gas with a relatively low percentage or in y some cases, entirely free of oxygen, and the gas is thus netter adapted for use for various purposes, particularly for use in the modified form of flow described in connection with bypass 5l. Also, in certain instances, particularly in catalytic cracking in the presence of aluminasilica type of cracking catalyst such as Super- Filtro the conversion reaction is facilitated by the presence of a small amount of residual carbon and in most instances the advantages obtained in regeneration by the maintenance of a residual carbon concentration will outweigh the disadvantages if any, resulting in the conversion stage. The residual carbon concentration maintained may depart somewhat from the value of 1.5% regarded as the approximate optimum in the foregoing example wherein a Super-Fil-trol type of alumina-silica cracking catalyst was employed. Preferably, this permissible range is confined to about 0.5% to 2.0%, by weight of the catalyst, or the narrower range of about 0.8% to 1.5%.

A number of highly advantageous results are secured by mixing the liquid feed stock with the regenerated catalyst while the latter retains the heat imparted to it in the regeneration reaction. Conventional methods for vaporizing and preheating the oil to the required conversion temperature would frequently result in substantial thermal decomposition or cracking, which is undesirable because of the low quality of products thus obtained, particularly with respect to octane number and ultimate amount of coke formed, compared with those produced by complete catalytic conversion. Due to the intimate contact between the hot catalyst and feed stock and resultant rapid and vefficient; vaporization, undesired thermal cracking is largely obviated. Substantial savings are further secured by the resulting direct use of the major proportion of heat evolved during the regeneration stage.

Any type of catalyst suitable for effecting the desired conversion may be employed in the practice of my invention. For the conversion or cracking of high-boiling fractions such as gas oil to low-boiling fractions such as gasoline, I regard cracking catalysts of the alumina-silica type as especially suitable, this term being inclusive of cracking catalysts such as certain 'types of activated clays or synthetically produced mixtures or compounds of alumina and silica. The circulated catalyst may be composed entirely of the active catalytic material and is preferably predominantly composed thereof.' However, the active catalyst material may be associated with supports, extenders or solid diluents which for the purpose of my invention are to be considered as part of the catalyst, since such solid diluents, etc., will function in a manner similar to the active part of the catalyst relative to the absorption of heat in the regeneration zone and the transfer of this heat `to the hydrocarbons undergoing treatment. When alumina-silica type of cracking catalysts are employed, the practice of my invention will usually involve catalyst-to-oil weight ratios greater than 2.5 to 1, and preferably greater than 5.0 to l.

In the modified type of flow described above in connection with bypass line 5| the total products of regeneration including the regenerated catalyst and combustion gases are returned of oxygen in the products of the regeneration is l thereby assured and objectionable introduction of oxygen into the conversion reaction thereby avoided.

In accordance with a further example of the practice of my invention, a naphtha having a gravity of 50.3 A. P. I. was subjected to a catalytic conversion treatment suitable for reforming the naphtha and increasing its octane number. In this treatment a dehydrogenating and cyclicizing catalyst was employed suitable for converting a large proportionof the aliphatic hydrocarbons in the charged stock to aromatic compounds. It was ascertained that conversion to the desired extent involved the formation of carbonaceous material to the extent of 0.8% by weight of the naphtha charged, and that the deactivation temperature of the catalyst was about 1050 F. The quantity of air necessary to supply the oxygen required to burn the carbonaceous material formed was suiicient to absorb 21.6% of the heat liberated in the combustion of the carbonaceous material as determined by computation based on the introduction of the air at a temperature of 100 F. and the Withdrawal of the regeneration and combustion gases at a temperature of 1050 F. In this reaction the temperature of the catalyst leaving the reaction zone was 925 F., and the'catalyst was introduced into the regeneration zone at substantially this temperature. The values of the symbols in the above described general formula in this example were accordingly as follows:

C :fraction of carbonaceous material produced=0.008

H :heat of combustion of carbonaceous mateterial=l6400 B. t. u. per lb.

S :specific heat of catalyst=0.22

T1=deactivation temperature of the catalyst=1050 F. Tz--temperature of catalyst entering the regeneration zone=925 F.

K :fraction of the total heat liberated in the regeneration absorbed by the catalyst=0.784

Substituting these values in the general formula to determine the desired ratioit is evident that this is 3.72 by the following equation:

jointly or separately. It will further be readily apparent to those skilled in the art that while the invention has been illustrated and described with respect to a preferred operation and examples, and with reference to suitable apparatus for its practice, the invention is not limited to such exemplications but may variously be practiced and embodied within the scope of the claimsv hereafter made.

`What I claim is:

1. A process for the catalytic conversion of hydrocarbons which comprises passing -a vapor stream of the hydrocarbons having the catalyst suspended therein throughK a conversion zone 4to effect the required degree of conversion, whereby reaction products are produced including converted hydrocarbons and a. carbonaceous deposit on the catalyst, maintaining a ratio by weight of catalyst to hydrocarbon charged to said conversion zone in conformity with the formula wherein the symbol C, represents the fraction of charged hydrocarbon converted to form carbonaceous deposit on the catalyst; H, the heat of combustion of the carbonaceous material expressed in B. t. u.s per 1b.; S, the specific heat of the catalyst; T1, the deactivation temperature of the catalystin degrees Fahrenheit; T2, the temperature of the catalyst on entering the regeneration zone in degrees Fahrenheit; and K, a coefficient having a value of 0.2 or larger, separating the used catalyst from the gaseous reaction prodi ucts and regenerating it by passage through a regeneration zone, while suspended 'in an oxygencontaining gas, withdrawing the regenerated catalyst from said regeneration zone and admixing it with liquid hydrocarbon feed stock while retaining suiiicient heat to vaporize the feed stock, and returning said catalyst in suspension in the vapors thus produced, to said conversion zone.

2. A process for vthe catalytic conversion of hydrocarbons which comprises passing a vapor stream of the hydrocarbons having the catalyst suspended therein through a conversion zone to eiect the required degree of conversion, whereby reaction products are produced including converted hydrocarbons and a carbonaceous deposit on the catalyst, maintaining a ratio by weight of catalyst to hydrocarbon charged to said conversion zone in conformity with the formula- Sum-T2) K wherein the symbol C, represents the fraction of charged hydrocarbon converted to form carbonaceous deposit on the catalyst; H, the heat of combustion of the carbonaceous material expressed in B. t. u.s per lb.; S, the specific heat of the catalyst; T1, the deactivation temperature of the catalyst in degrees Fahrenheit; T2, the temperature of the catalyst on entering the regeneration zonevin degrees Fahrenheit; and K,

a coeiiicient having a value of 0.2 or larger, separating the used catalyst from the' gaseous reaction products and regenerating it by passage through a regeneration zone, while suspended in an oxygen-containing gas, withdrawing the regenerated catalyst and regeneration combustion gases from said regeneration zone and mixing them with the liquid hydrocarbon feed stock while retaining suilicient heat to vaporize the feed stock, and returning said catalyst in suspension in the vapors thus produced to said conversion zone.

3. In a process for the catalytic conversioirpf high-boiling hydrocarbons into low-honing hydrocarbons within the gasoline boiling range involving passing a stream of the high-boiling hydrocarbons having a cracking catalyst comprising alumina and silica suspended therein through a conversion zone for a time and at a temperature adapted to eliect the required degree of con-- version to low-boiling hydrocarbons and also re r wherein R, represents the maintained ratio; C, represents the fraction of charged hydrocarbon converted to form carbonaceous deposit on the catalyst; H, the heat of combustion of the carbonaceous material expressed in B. t. u.s per lb.; S, the specific heat of the catalyst; T1, the deactivation temperature of the catalyst in degrees Fahrenheit; T2, the temperature of the catalyst on entering the regeneration zone in degrees Fahrenheit; and K, a coefficient having a value greater than 0.2, and introducing the used catalyst into the regeneration zone with a quantity of oxygen-containing gas insuiiicient to burn of! all the carbonaceous material thereby leaving a predetermined small residual quantity of carbonaceous material on the catalyst as discharged from said zone and reused in the conversion zone.

4. In a process for the catalytic conversion of high-boiling hydrocarbons into low-boiling hydrocarbons within the gasoline boiling range involving passing a stream of the high-boiling hydrocarbons having a solid incombustible cracking catalyst suspended therein through a conversion zone for a time and at a temperature adapted to effect the required degree of conversion to low-boiling hydrocarbons and also resulting in a carbonaceous deposit on the catalyst, separating the used catalyst from the vaporous conversion products, suspending the used catalyst in an oxygen-containing gas and passing the suspension through a regeneration zone to burn off carbonaceous material deposited on the catalyst, and returning the catalyst for reuse in the conversion reaction, the improvement which consists in introducing the used catalyst into the regeneration zone with a quantity of oxygen-containing gas insuiilcient to burn oi all the carlbonaceous material thereby leaving a predetermined small residual quantity of carbonaceous material on the catalyst as discharged from said zone and reused in the conversion zone.

5. In a continuous cyclic process for the catalytic conversion of high-boiling hydrocarbons into low-boiling hydrocarbons within the gasoline boiling range involving continuously passing a stream oi?"the'high-boiling hydrocarbons having a cracking catalyst suspended therein through a conversion zone for a time and at a temperature adapted to effect the required degree of conversion to low-boiling hydrocarbons and also resulting in a carbonaceous deposit on the catalyst, continuously separating the used catalyst from the vaporous conversion products, continuously suspending the separated used catalyst in an oxygen-containing gas and passing the suspension through a regeneration zone to burn oiT carbonaceous material deposited on the catalyst, and directly and continuously returning the catalyst for reuse in the conversion reaction, the improvement which consists in maintaining a ratio by Weight of catalyst charged to said regeneration zone to weight of hydrocarbon charged to said conversion zone in conformity with equation CH Sun-T.) K

wherein r represents the maintained ratio; C represents the fraction of charged hydrocarbon converted to form carbonaceous deposit on the catalyst; H, the heat of combustion of the carbonaceous material expressed in B. t. u.s per lb.; S, the specific heat of the catalyst; T1, the deactivation temperature of the catalyst in degrees Fahrenheit; T2, the temperature of the catalyst on entering the regeneration zone in degrees Fahrenheit; and K, a coefcient having a value greater than 0.2.

6. A process as deiined in claim 5 wherein said symbol K is a number 0.5 or larger.

7. A process as defined in claim 5 wherein said symbol K, is a number not less than 0.8 and the used catalyst is introduced in said regeneration zone suspended in air in quantity sufficient only to supply the quantity of oxygen theoretically required to burn off carbonaceous material leaving a predetermined small residual quantity of carbonaceous material on the catalyst as discharged from said zone and reused in the generation zone.

8. A process as deiined in claim 5 wherein said symbol K is a number 0.5 or larger and said cracking catalyst consists essentially of alumina and silica.

ARNOLD BELCHETZ. 

